engines that were specifically designed and manufactured to be turbocharged and supercharged are generally rated at lower 'compression ratios' compared to naturally aspirated engines. This is because the forced introduction of fuel/air into the combustion chamber raises the 'ratio' dramatically. If you raise the pressure inside of the cylinder too much, you will enter the problem area where pre ignition or pre detonation occur during periods of heavy load and high operating temperature. Higher octane fuels reduce this issue in a gasoline engines. Most cummins diesel engines of recent manufacture are turbocharged. They have a 'dished out' area on the crown of the piston head that forms the lower portion of the combustion chamber and lowers the 'compression ratio' from what having a flat top or crowned piston would deliver. Compression Ratio alone as a term can be mis-understood. The term only figures the change in volume of the cylinder from BDC (bottom dead center) to TDC (top dead center)with no allowances for the speed of piston travel or the volummetric efficiency of the air intake system. for example if the cylinder and combustion chamber in the head has a volume of 100 CC's at the bottom of the stroke and 1 cc at the top the 'ratio' will be expressed at 100:1.
--- In [EMAIL PROTECTED], "harmonseaver" <[EMAIL PROTECTED]> wrote: > --- In [EMAIL PROTECTED], Christopher Witmer <[EMAIL PROTECTED]> wrote: > > What is the significance of diesel engine compression ratio in a > > cogeneration context? I have heard that with cogeneration, the higher > > the compression ratio the better. Can anyone tell me why? Is it because > > a higher compression ratio means more heat? And how high is "high" for > > readily available engines? I think my source said something to the > > effect that Cummins has some engines with relatively high compression > > ratios, beyond 20:1. Also, how easy is it to increase an engine's > > compression ratio? I seems to me that one could damage one's engine > > trying, if one was careless. > > I don't think it makes any difference in "cogeneration", per se, > the engines still run at the same operating temperature. Perhaps what > you are thinking of is that engines running on biomass gasifiers need > much higher compression, which is why diesels are used. Many diesels > have 25:1 compression, although some newer ones like the VW TDI's have > only about 18:1. > You can quite easily raise compression ratio by having the > cylinder head milled off a bit, although that needs to be done after > careful computation of the deck height of the pistons in the cylinder > and the actual volume of the compression chamber in the head. For some > gasoline engines, high compression pistons are available, although > those are probably only going to take it to 11:1 or 12:1. Even for > ethanol you want at least 13:1. > You can't raise it much more than that for a petrol engine, since > the piston crowns and connecting rods aren't strong enough. Bearings > also might be a problem. Better to use a diesel and convert it to > spark if necessary. ------------------------ Yahoo! Groups Sponsor ---------------------~--> Sell a Home for Top $ http://us.click.yahoo.com/RrPZMC/jTmEAA/MVfIAA/FGYolB/TM ---------------------------------------------------------------------~-> Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Biofuels list archives: http://archive.nnytech.net/ Please do NOT send Unsubscribe messages to the list address. To unsubscribe, send an email to: [EMAIL PROTECTED] Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
